1. Field of the Invention
The present invention generally relates to sensors for detecting gaseous components in gaseous environments containing same, to novel sensing materials useful in such sensors, and to semiconductor manufacturing process systems comprising such sensors.
2. Description of the Related Art
In the field of semiconductor manufacturing, wafer substrates are processed in reactor vessels in a variety of unit operations, such as deposition of thin film materials, e.g., by metalorganic chemical vapor deposition (MOCVD), etching (of the wafer and/or microelectronic device structures fabricated thereon), plasma treatment, ion implantation, etc. In addition, the reactor vessel itself may be subjected to cleaning by operations such as chamber etching, solvent flow-through, and elevated temperature volatilization of deposits.
The aforementioned operational functions are typically conducted for a given amount of time, as opposed to determining an endpoint for the process step by monitoring of process parameters with appropriate instruments. Accordingly, there is an absence of real-time control of these operational functions. Such lack of real-time control results in process inefficiencies. Further, there are few available reliable and inexpensive methods to follow the progress of a reaction in the reaction vessel. Test wafer and exact process control are usually the approach employed to gate the time of a process step.
In application to plasma-based processes, the art recently has proposed the use of optical emission spectroscopy (OES) and radio frequency (RF) impedance monitoring to detect changes in a plasma above a wafer, to demarque the end-point of the plasma-based process. Such approaches have significant deficiencies in practice, however. OES systems are prone to fogging of the optical windows employed in such systems, with consequent signal loss. RF impedance systems are highly sensitive to all changes in the overall state of the process, not just those of particular interest. Further, both OES and RF impedance systems depend on the presence of a plasma for their respective signals.
There is therefore a need in the art for a chemically selective device that provides the capability of endpoint monitoring without requiring the presence of a plasma.
More generally, in the field of gas monitoring, the art has employed various gas component detectors. Examples include pyrometric sensors, infrared and spectrophotometric detectors, gas chromatographic analyzers, and piezoelectric microbalances including quartz microbalances (QMBs) and surface acoustical wave devices (SAWs).
In some systems, a multiplicity of QMBs are employed for sensing of components of a multi-component gas stream, wherein each of the QMBs is coated with a specific sensor coating having affinity for a selected component or group of components of the multicomponent gas stream. In other instances, a single QMB may be used for detecting a single critical component of a multi-component gas stream.
A problem with the use of such QMB systems is that the means used to hold the crystal element(s) in position in the sensor device assembly are not very robust physically, and are not intended to be used in harsh environments, e.g., corrosive or otherwise chemically reactive atmospheres. Presently employed componentry typically uses glass to metal seals, steel wire, and silver epoxy for effecting electrical contact to the QMB element. All of such components fail in prolonged service in harsh environments.
It therefore would be an advance in the art to provide a holder or support structure for QMB elements that overcomes the aforementioned deficiencies.
In the art of QMB technology, it is known to coat a QMB element with a porous matrix coating, to provide an open material structure for interaction with gas component(s) of a gas stream or gas environment contacted with the QMB element. U.S. Pat. No. 5,827,947 issued Oct. 27, 1998 to Cindy Miller, et al. for "PIEZOELECTRIC SENSOR FOR HYDRIDE GASES, AND FLUID MONITORING APPARATUS COMPRISING SAME" discloses a sensor for detection of a trace fluid component in a fluid environment, comprising a piezoelectric crystal having a fundamental resonant frequency in response to an applied oscillating electric field, and an inert porous material coating on the piezoelectric crystal. The inert porous material coating contains a metal species that is reactive with the trace fluid component to yield a solid interaction product of changed mass in relation to initial mass of the metal species interacting with the trace fluid component to yield the solid interaction product.
It would be an advance in the art to provide an improved porous film material for use in forming an affinity coating on a QMB surface, for gas sensing applications.
It is an object of the present invention to provide sensing means, device structures and systems that in various embodied forms overcome the above-mentioned deficiencies of the prior art.
It is another object of the present invention to provide improved quartz crystal microbalance sensors for detecting gaseous components in gas mixtures containing same.
It is a further object of the invention to provide an improved semiconductor manufacturing process system comprising one or more QMB sensors.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.